Phosphorus containing iron powder



United States Patent 3,497,347 PHOSPHORUS CONTAINING IRON POWDER NorbertDautzenberg, Lank-Niederrhein, Gerhard Naeser, Duisburg-Huckingen, andGerhard Findeisen, Rheydt, Germany, assignors to MannesmannAktiengesellschaft, Dusseldorf, Germany, a corporation of Germany NoDrawing. Filed Aug. 28, 1967, Ser. No. 663,524 Int. Cl. B22f 1/00; C22c39/54 US. Cl. 75.5 2 Claims ABSTRACT OF THE DISCLOSURE An iron powderthat contains phosphorus, and is used in forming sintered pressedarticles that have a high degree of strength and are shrink free duringsintering, vis composed of a mixture of two iron powders one of whichhas a large content of phosphorus and the other has but a minute contentof phosphorus.

The invention relates to phosphorus containing iron powder, for use informing therefrom sintered pressed articles that have a high degree ofstrength and, during sintering, are free from shrinkage.

Sintering, for use in the mass production of accurately dimensionedarticles composed of iron and steel, has successfully joined the groupof noncutting shaping processes. Although the knowledge gained ingeneral steel metallurgy is not of much use for the development of thenew sinter steels, sinter steels have been produced that maintainindustrially a tensile strength of up to 60 kiloponds per squaremillimeter. Copper, nickel and carbon, the latter as an additive in theform of graphite, have been used successfully as alloying elements insuch sinter steels. Among the drawbacks of using copper and nickel inhigh grade sinter steels has been found to be the high cost of copperand nickel; furthermore, it has been found that the degree of elongationat rupture that may be achieved in such sinter steels lies far below thevalue of a comparable-steel obtained from a molten steel mass. Thedegree of elongation at rupture of sinter steels may be increased, butonly with the aid of expensive operational steps, such as doublepressing and double sintering, or hot pressing, and the like.

It is known that sinter iron with a high content of phosphorus of from.3 to .8 percent by Weight, though with a low carbon content preferablybelow .02 percent by weight, has good tensile strength and elongation atrupture characteristics. In the literature there have been proposedmixtures of soft iron powder with the following additives: powders ofred phosphorus, iron phosphate, or ground ferrophosphorus with fromabout 14 to about 18 percent by weight of phosphorus (P).

Experiments have furthermore been made with prealloyed powders, thathave been made by atomizing of melts, or by machining.

The best strength values and elongation values, however, have beenachieved with a phosphorus content of about .5 percent by weight. Forinstance, elongation rupture rods have been tested and found to have thefollowing values, after a one-hour sintering at 1200 C., at a phosphoruscontent of .52 percent by weight and a carbon content of .01 percent byweight, and remaining impurities of less than 1.0 percent by weight:

Tensile strength-39.0 kiloponds per square millimeter Elongation atrupture.l4.5 percent Density.6.91 grams per cubic centimeter Change insize as compared to the matrix A1=2.10 percent (linear).

Comparable sinter steels alloyed with copper and nickel ice would yieldan elongation at rupture of about 5 percent, though would have a changein size of about .10 percent.

As the advantages of sintering prominently include the fact thatarticles can be manufactured to theoretical size, the large change insize of the ferrophosphorus is a material drawback, particularly as thechange in size of the powder mixtures mentioned in the foregoing rangesbetween 5 and 20 percent, and even for the aforementioned pre-alloyedpowders still has a range of change in size of 2 to 3 percent. The largeshrinkage may be due to an occurrence of a liquid phase during sinteringand the Fe P/Fe-eutectic. The excellent strength values of this materialwould promise wide acceptance in the field of production to accuratesize if it were possible to suppress the large changes in size mentionedhereinbefore; in that case the ferrophosphorus would be acceptable as anequal with the copper alloyed and the nickel alloyed sinter steels, butwould have a much better elongation characteristic and, notably, wouldhave the further great advantage of being less expensive. It wouldmoreover have the advantage that such a phosphorus containing iron wouldobtain its desirable properties after a single pressing and sintering,and furthermore would be characterized by an easy machinability.

The instant invention accordingly has among its principal objects toprovide a phosphorus containing iron powder that retains unchanged thestrength and elongation characteristics of such powders of the priorart, and yet to reduce as much as possible the disadvantageous changesin size that had heretofore characterized articles made from theaforesaid powders.

Further objects and advantages of the invention will be set forth inpart in the following specification and in part will be obvioustherefrom without being specifically referred to, the same beingrealized and attained as pointed out in the claims hereof.

Generally, the instant invention achieves the aims by providing aphosphorus containing iron powder that comprises a mixture of two ironpowders, one of which has a high content of phosphorus, and the other acontent of phosphorus that is as low as possible. The entire content ofphosphorus of the mixture preferably is between .2 and 1.4 percent byweight, with a preferred range of between .3 and .8 percent. The shareof the phosphorus lean iron powder of the mixture is from 30 to 90percent by weight, preferably between 60 and percent by weight; and thephosphorus rich powder of the mixture contains less than 5 percent byweight of phosphorus, while the phosphorus lean iron powder containsonly about .03 percent by weight of phosphorus.

The content of phosphorus of the phosphorus rich iron powder, however,must not be materially in excess of 3 percent by weight, as otherwise,as at the ferrophosphorus addition during sintering, there may occur aliquid phase that would cause a large change in size. It has been foundthat surprisingly the change is size of pressed articles from the steelpowder mixtures of the invention is much smaller than of comparablepressed articles made from alloyed steel powders. Yet the sintered partsmade from the mixed powders, and those made of the alloyed powders, havethe same mechanical properties; the powder mixture therefore must becompletely homogenized.

EXAMPLES In the examples below, a powder mixture is used that has anoverall content of .5 percent by weight of phosphorus, and that iscomposed of normal phosphorus lean iron powder that has a content of .03percent by weight of phosphorus, and an iron powder that is alloyed withhosphorus. The strength of sintered articles made there- 3 from rangesfrom 38 to 40 kiloponds per square millimeter; for the different mixingproportions, however, there are found to exist different changes insize, as set forth in the table below:

Powder (percentages Changes in size, by weight): (percent) (1)Homogenous powder 2.10

(2) Mixture: 50% soft iron, 50% soft iron with 1% P -.9S

(3) Mixture: 66.6% soft iron powder,

33.3% iron powder with 1.5% P (4) Mixture: 90% soft iron powder, 10%

iron powder with 5% P l2.4

As a comparison between the powders 1), (2) and (3) reveals, the instantinvention provides that by the use of powder mixtures there can beachieved very small changes in size during sintering. It is only withthis small change in sizes that it becomes possible to utilize fortechnical advantage, for powder metallurigic-al purposes, the excellentproperties of carbon lean, phosphorus containing powder steels. Theunexpectedly large reduction in shrinkage probably may be explained dueto the so-called Kirckendahl effect. The example (4) of the above tableshows that, probably due to the occurrence of a liquid phase, themixtures heretofore used of soft iron powder and ferrophosphorus powderyield too large changes in size.

We wish it to be understood that we do not desire to be limited to theexact details described, for obvious modifications will occur to aperson skilled in the art.

Having thus described the invention, what we claim as new and desire tobe secured by Letters Patent, is as follows:

1. A phosphorous iron powder mixture, for use in producing sinteredpressed articles having a high degree of strength and beingsubstantially shrink-free during sintering, of from to 90 percent byweight of the mixture consisting of one iron powder type having aphosphorus content of about .03 percent, the remainder of the mixtureconsisting of a second iron powder type having a phosphorus content ofless than 5 percent wherein the total phosphorus content of the mixtureis between .2 and 1.4 percent by weight.

2. A phosphorous iron powder, as claimed in claim 1, said one typepowder forming of from to 80 percent by weight of the mixture.

References Cited UNITED STATES PATENTS 2,213,523 9/1940 Jones et al.-123 2,661,282 12/1953 Daley 75-123 FOREIGN PATENTS 571,442 8/ 1945Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner T. R. FRYE, Assistant Examiner US.Cl. X.R. 75-l23

